The serious complications of myelography with aqueous media are seizures and arachnoiditis. Post myelographic arachnoiditis decreases the safety and value of any subsequent myelography and may produce pain and neurologic disability. The pathogenesis of post myelographic arachnoiditis has not been adequately studied. Arachnoiditis following experimental metrizamide or meglumine iocarmate myelography will be studied in a primate model. In this mode, post myelographic arachnoiditis can be detected and quantitated. The objectives of the study are to determine; 1) the severity of arachnoiditis in relation to the type and amount of myelographic contrast medium employed, 2) the effect of different myelographic techniques on the severity of arachnoiditis, 3) the modification of post myelographic arachnoiditis by intrathecal anti-inflammatory drugs or bloody cerebrospinal fluid, and 4) the pathogenesis of post myelographic arachnoiditis. Myelography will be performed in macaque monkeys with techniques which simulate clinical lumbar myelography. Following a myelogram, the animal will be observed for twelve weeks. After observation, the myelogram is repeated to idnetify myelographic changes of arachnoiditis. Then the animal is sacrificed and the dural sac and its contents are dissected, sectioned, stained and the specimen is examined for evidence of arachnoiditis. Techniques for examination of the arachnoid include polarizing light microscopy, electron microscopy, immunofluorescent staining. Because of the similarity of myelography and arachnoiditis in primates and in humans, recommendations can be made on the basis of this study as to safe, effective doses of water-soluble contrast media. Successful identification of the pathogenesis of post myelographic arachnoiditis may permit the synthesis of improved aqueous contrast media.